Cymbella excisa Kützing

Joh, Gyeongje, 2025, The seven species of the genus Cymbella (Bacillariophyta), previously unknown from the inland water of South Korea, Journal of Species Research 14 (1), pp. 6-19 : 8-11

Cymbella excisa Kützing var. excisa ( Figs. 24-34 )

Synonyms. Cymbella affinis f. excisa (Kützing) Grunow 1882 ; Cymbella affinis sensu Reimer in Patrick and Reimer 1975 (excluding synonyms and morphometrical values); Cymbella affinis sensu Krammer and Lange-Bertalot 1986 .

Non synonym. Cymbella affinis Hustedt 1930 .

Reference. Krammer, 2002, p. 26, pl. 5, fig. 1, pl. 8, figs. 1-26, pl. 9, figs. 19-25, pl. 12, fig. 7.

Description. Valves moderately dorsiventral, dorsal margin strongly arched, ventral margin straight to weakly convex or tumid, or frequently sunken in the center. The ends of valve subrostrate to rostrate. Valves 24-35 μm long, 8-9 μm wide. Raphe lateral, becoming reverse-lateral near the proximal ends of the raphe and near the distal ends. Striae 9-12 in 10 μm in the center, areolae 26-30 in 10 μm. Isolated and large one stigma in the middle of the ventral side.

Diagnoses. Cymbella excisa was described as a scientific name by Kützing (1844), but Krammer (2002) emended it taxonomically by organizing the morphological range of February 2025 Joh. The previously unknown species of the genus Cymbella 9 the species and establishing its relationship or boundary with other neighboring taxa. This species is similar to several taxa belonging to the excisa/parva group defined by Krammer (2002) in the genus Cymbella in terms of the outline and dimensions of valve, and its morphology. Cymbella excisiformis Krammer is very similar to C. excisa in the outline of the valve and the shape of apices, but differs in the dimensions of the valve. In the ratio of the length and width of the valve in the former species ranges from 4.2 to 5.3, which is greater than that of the latter (from 2.9 to 4.1). Cymbella excisa resembles to the smallsized ones among C. parva Krammer ( Krammer, 2002), but the latter is distinguished from the former in that the apices of the valve is not protracted. Cymbella perparva Krammer also differs from C. excisa in the shape of the apices. On the other hand, C. exigua Krammer differs from C. excisa in that the density of striae is relatively dense, at 15-17 in 10 μm.

1 2 3 6 8 7 4 5 9 10

Occurrence. Cymbella excisa was found frequently at the two places through this study, the reach of the Namhan River in Danyang and the Ian Stream in Sangju. In addition, this species has observed commonly in the flowing sections of streams and rivers in other regions. It is cosmopolitan worldwide as the epilithon and epiphyton in stagnant and flowing inland waters, and abundant in the mountain ( Krammer, 2002).

Figures

Figs. 24-34. Cymbella excisa. 24-30. Valve view under LM, showing the size variation of valves. 31-34. Valve view under SEM, and one large stigmata on the ventral side of the valve. 31, 32. The strongly reverse-lateral deflection of the proximal raphe ends. 33, 34. The internal view of the valve. Stigmata and central nodule at the central parts of the valve. Scale bars=10 μm(24-30); 4μm (31, 34); 2 μm(32, 33).